1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification, the semiconductor device generally means any device which can function by utilizing semiconductor characteristics, and an electrooptic device, a semiconductor circuit, and electronic equipment are all included in the category of the semiconductor device.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor with use of a semiconductor thin film formed over a substrate having an insulating surface (the transistor also referred to as a thin film transistor (TFT)). The transistor has been applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). A silicon semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor has attracted attention.
As for the transistor using an oxide semiconductor, better electric characteristics has been required for application to semiconductor devices with higher performance. To realize good electric characteristics of a transistor using an oxide semiconductor, for example, a technology in which a low-resistance source and drain regions are formed by using an aluminum reaction method has been reported (e.g., see Non-Patent Document 1).